Lagerstroemia Red Dynamite – Red Crepe Myrtle are a very fast growing tree that fills with gorgeous clusters of true red blooms from July to September, and both beautiful, hearty, and very drought resistant once established. These red crape myrtles produce 6” to 12” clusters of red flowers that can last for many weeks or even months are a very fast growing tree that fills with gorgeous clusters of true red blooms from July to September, and both beautiful, hearty, and very drought resistant once established. These red crape myrtles produce 6” to 12” clusters of red flowers that can last for many weeks or even months.